Ureteral stents are used to create a pathway for urinary drainage from the kidney to the bladder in patients with ureteral obstruction or injury or to protect the integrity of the ureter in a variety of surgical manipulations. A number of clinical conditions can produce interruption in urine flow including, for example, intrinsic obstruction of the ureter due to tumor growth, stricture or stones, compression of the ureter due to extrinsic tumor growth, stone fragment impactation in the ureter following extracorporeal shock wave lithotripsy (ESWL), and ureteral procedures such as ureteroscopy and endopyelotomy. Stents may be used to treat or avoid obstructions of the ureter (such as ureteral stones or ureteral tumors) that disrupt the flow of urine from the corresponding kidney to the urinary bladder. Serious obstructions of the urinary tract may cause urine to back up into the kidney, threatening renal function. Ureteral stents may also be used after endoscopic inspection of the ureter. The stent may be placed in the ureter to facilitate the flow of urine from the kidney to the bladder and to enable the ureter to heal.
Ureteral stents typically are tubular in shape, terminating in two opposing ends: a kidney distal end and a urinary bladder proximal end. One or both of the ends of the stent may be coiled in a pigtail spiral or J-shape to prevent the upward and/or downward migration of the stent in the lumen of the ureter due to, for example, day-to-day physical activity of the patient. A kidney end coil is designed to retain the stent within the renal pelvis and to prevent stent migration down the ureter. A urinary bladder end coil is positioned in the bladder and is designed to prevent stent migration upward toward the kidney. The bladder end-coil is also used to aid in retrieval and removal of the stent.
A ureteral stent assists in the flow of urine from the kidney to the urinary bladder. The region known as the trigone is an area that surrounds the ureteral orifices at the insertion of the ureters into the bladder and extends to the bladder neck at the urethral outlet of the bladder. The trigone has greater pain sensation relative to other regions of the bladder wall and is a major source of patient discomfort when the typical indwelling stent is in contact with this region of the bladder.
Ureteral stents may be introduced to the body either percutaneously in an antigrade fashion, using for example, an adaptation of the Seldinger technique, or cystoscopically in a retrograde fashion. The stents positioned in the bladder through a cystoscope are passed into the ureter using direct vision through the endoscope positioned in the bladder. For placing the stent, there are two conventional techniques. A guidewire of sufficient stiffness and maneuverability is inserted into the ureter under endoscopic guidance. When access past the ureteral obstruction of the kidney is achieved, the stent is introduced to the ureter over the wire by a pusher catheter acting on the trailing or proximal edge of the stent.
The second conventional placement method for ureteral stents omits the prior step of placing a guidewire and may be used where no large obstruction is present. In this method, the guidewire is inserted through the stent only until it is flush with or within the tip the stent. A pusher catheter is again inserted behind the stent on the guidewire and is locked to the guidewire with a locking hub (e.g., SPEED-LOK® product available from Boston Scientific Corporation, Natick, Mass.). The assembly is then pushed by the pusher catheter acting on the proximal end of the stent to enter the cystoscope and then the ureter.
Ureteral stents, particularly the portion positioned in the ureter and the bladder, may produce adverse effects including hemorrhage, a continual urge to urinate, flank pain accompanying reflux of urine back up the ureter due to retrograde pressure when voiding, and chronic trigone and flank pain. Chronic trigone irritation resulting from contact by the bladder anchoring features of the stent or resulting from intraoperative trauma inflicted from passage of the device in the ureter.
Flank pain may be caused from typical ureteral stents during urinary voiding. On the initiation of voiding the bladder wall muscles contract causing the pressure inside the bladder to rise. Because a typical indwelling ureteral stent holds the ureteral orifice open, this pressure is transmitted to the kidney causing the patient to experience flank pain. Attempts to mitigate some of these problems associated with ureteral stents include administering systemic pharmaceuticals such as anti-spasmodic drugs which may present additional undesirable side effects. In general, ureteral stents may cause or contribute to significant patient discomfort and serious medical problems.